Nonseismic torsiograph



Sept. 1'6, 1952 L. F. HOPE 2,610,505

NONSEISMIC TORSIOGRAPH Filed March 18, 1949 Snveutor Patented Sept. 16, y1952 NoiqsEIsMIo ToRSIoGnArn Lawrence F. Hope, Grosse Pointe Farms, Mich.,

assigner to General Motors Corporatiorunetroit, Mich., a corporation of Delaware Application March 18, 1949, Serial No. 82,220

The present invention relates to means for measuring torsional vibration frequency and amplitude. More particularly it relates to nonseismic means for measuring these quantities.

Torsional vibration is not a new problem and engineers have previously developed instrumen-` tation for measuring this type of vibration under certain conditions. Most torsiographs however depend on a seismic mass or an electrical circuit giving equivalent results in determining torsional vibration frequency and amplitude. Such measuring instruments have two inherent limitations, one being minimum vibration frequency and the other being maximum vibration amplitude. It would, for example, be quite difficult to design a conventional type instrument capable of measuring torsional oscillations having an amplitude of 20 degrees with a frequency of .5 cycleper second. Conventional torsiographs have either mechanical or electrical stops which must be `sufciently spaced to include the greatest am-` Aoccuring below the idle speed of an internal combustion engine.

It is therefore an object of the present invention to produce a torsional vibration measuring instrument cac-able of responding to angular velocity deviations of low frequency and high amplitude.

It is a second object of the present invention to produce a torsional vibration measuring instrument requiring no seismic mass.

It is a third object of the present invention to produce a torsiograph which is simple in operation and accurate in results. l e

It is a further object of the present invention to provide a torsiograph which will operate satisfactorily over a large range of mean speeds with a minimum of correction for mean speed.

It is a still further object of the present invention to provide a torsiograph the output signal of which is proportional in amplitude and equal A conventional design torsiograph withA a claims. (oi. 'z3- ssi in frequency to the torsional vibration of the mass under investigation.

Other objects of the present invention will become apparent upon reading of the specification and inspection of the drawing and willbe specifically pointed out in the claims.

Referring to the drawing:

Figure 1 is a schematic showing of the present invention.

Flgure`2 shows wave forms at various points in the circuit illustrated in Figure 1.

Figure 3 shows certain Wave forms on a dif ferent time scale than Figure 2.

Referring more particularly to Figure 1, 2 is shaft the torsional vibration characteristics of' which it is desired to determine. Rigidly secured to that shaft is a gear type signal generator '4.' The gear in this generator is subject to al1 the torsional vibration and other physical movements of the shaft 2 occurring` at the point to which` the gear is secured. Pickup coils 6 and 8 are' mounted in stationary relation to the'frame in which the shaft 2 rotates. These two pickup coils are located diametrically opposite ea'ch other and generate sinusoidal signals in aiding phase at gear tooth passage frequency. They purpose of using two pickups is to minimize the effect of gear wobble in a plane normal to the axis of rotation. Each time a gear tooth passes the pole of pickups E and 8, one cycle of alternating voltage is generated. A signal I0 is thereby generated and applied at point 9 of frequency i equal to the number of teeth on the gear' times the rotational frequency ofthe shaft 2. This carrier signal I0 is phase modulated by torsional vibration. It is operated upon electrically as will be described later to produce a voltage proportional to lthis gear tooth passage frequency.V An" integration of this voltage yields a signal output voltage which is proportional to vibration ampli--y tude.

Referring more particularly to the circuit, the combined signal output l0 of the pickups 6 and 8 is fed into an overdriven ampliercircuit including tubes l2 and i4, resistors I8, 2|),` 22, 24, 26, 28 and 3U and condenser 32 to produceV a square wave I6. The square wave I6 is of constant amplitude and equal in frequency to the frequency of the pickup output signal ID; This signal is produced by standard electronic methods as will be noted from the circuit.

The'signal I6 which appears at the point 3i is fed into a differentiating circuit including condenser 36 and resistors 38, 40, and 42 to produce positive pips at the beginning of each square `Wave cycle I6. This circuit also produces negative pips `at the end of each square wave cycle but the negative pips are not used and are of no importance in the present invention. The pips are -amplied by an amplifier including tubes 44 and 46 and resistors 48, 50, 52 and 54 to produce positive potential pips 56 of sufficient amplitude to trigger a constant energy pulse square wave generator of the one shot multivibrator type. This circuit includes tubes 51 and 59, coupling condensers 58 and' 6| and resistors 60, 62, 64, 66 and 68. The tube 59 is normally conducting but, upon energization by the positive pips 56 applied to tube 51, the tube 59 is made non-conducting for a xed period of time after which'it returns to its conducting state. The output at the point 10 therefore consists of constant energy pulses 12 spaced from each other an amount proportional to the wave length of the signal or inversely to the frequency of this signal and the instantaneous angular yvelocity of the shaft 2. The resultant wave formed by the train of constant energy pulses actually'contains three components: (l) a D. C. voltage which is proportional to the steady speed of the gear generator which is unwanted; (2) a slow A. C. voltage which isproportional to velocity fluctuations and which provides the desired signal and is derived from a variation of the D. C. voltage above and below said steady speed; and (3) a higher frequency A. C. due to the pulses 12 themselves which is also unwanted. Provision is, therefore, made to remove the D. C. and higher frequency A. C. and utilize the signal whose. amplitude is proportional to torsional vibration amplitude; that is, proportional to the instantaneous angular displacement of' shaft 2 from its lnormal angular position Withuniform rotation ,which is obtained from the slow A. C. voltage. In order to remove the higher frequency A. C.- from this resultant signal, the constant area pulses are first passed through a low pass filter ycircuit including resistor 'I3 and condenser 14 (or condensers 'I4 and 16 depending upon the position of the range switch T8). Choke coil 82 and condenser 84 are utilized with the switch 86 in the position shown. If the switch is placed in the position opposite to that here shown, the choke coil 82 is combined with choke coil 8-8 and condenser l90 to produce this filtering action. The

direct current component of this vsignal is now removed by coupling condenser |00. There now remains only the slow or loW- frequency A. C. which is transmitted through condensen`j |00 and which produces a signal 92 at the point 94 as shown in Figures 2 and 3 on a reduced time scale.

The signal 92 has a frequency equal to the frequency of the torsional vibration oscillations.

The amplitude of the signal is a function of the instantaneous angular velocity of the gear generator 4. If the pulses 'l2 occur closer together. then the slow A. C. voltage will be higher or of greater amplitude, whereas if they are spaced farther apart the A. C. voltage will be less, and it is this cha-ngein spacing of the pulses 12 on the horizontal base line caused by torque vibrations that provides the slow A. C. and the signal 92, which has a frequency equal to the frequency of the torsional vibrations. Thus, as the pulses 'l2 in Figure 2 become more closely spaced at the right, the curve 92 acquires a higher amplitude which will reach a 4maximum when the pulses '|2 are closest together and then start to diminish as the pulses begin to widen in spacing, which compression and widening occur cyclically at the frequency of the torsional vibrations. The other A.. C. andAD. C. components of the wave train have at this point been removed. If, for the purpose of discussion, we assume the torsional vibration is sinusoidal, the signal amplitude is a function of both frequency and amplitude of torsional oscillation. The amplitude of the fluctuation or A. C. component of the signal may be represented as:

Instantaneous amplitude of signal 92=0 cos et 0 in radians per sec.=6.2832 times the torsional vibration frequency, in cycles per sec.

=constant depending on electrical design of circuit and on vibration amplitude t=time in seconds It is quite desirable that the amplitude of the. signal viewed be insensitive to frequency and a function of only the torsional oscillation amplitude. This transformation may be accomplished by integrating the signal l92 with respect to time after amplifying this signal by an amplifier including tube 98 and plate load resistor |06. This amplifier increases the amplitude of the signal 921 sufficiently for it tobe accurately integrated.

The signal after amplification is then integrated by means of integration circuit including resistor |08 and condensers ||0 and ||2. The condenser |||l may be shorted out by a switch ||4 if desirable to change the working frequency Instantaneous amplitude of signal |36v at the point |35 I :fo cos @tdt :Il: Sin. 0f

It may thus be seen that the peak amplitude of the signal |36 is insensitive to frequency and directly proportional to torsional vibration amplitude as was desired. This signal-:|36 is fed into an amplifier including tube ||6, coupling condenser ||8 and resistors |20, |22 and |24. The output of this amplifier is fed into a second amplifier'having tube |26, coupling condenser |28 and resistors |30, |32 and |34 to produce a signal |4| at the point- |38 proportional to the signal |36 and one which is equal in frequency and proportional in amplitude to the torsional oscillation of the shaft 2. The amplitude and frequency of the signal |4| may then be read on the cathode .ray oscilloscope |40 or by other suitable means. It is of course understood that the switches 18, 86 and ||4 are used to obtain the correct integrating and filtering action for the specific range of torsional vibration amplitude and frequency under measurement.

It is. to be understood also that although the invention has been described with specific referance to a particular embodiment thereof, it is ndt to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

I claim:

l. A non-seismic torsiograph including; an electrical signal generating means capable of generating an electrical signal of frequency directly proportional to the angular speed of a rotating body the characteristics of which it is desired' to determine, means for generating equal energy unidirectional pulses from said first mentioned signal whose pulse repetition frequency is proportional to said alternating current signal, means for electrically detecting said equal energy pulses to obtain a signal and means to integrate said last mentioned signal to produce a signal proportional in amplitude and equal in frequency to the torsional vibration being measured.

2. A non-seismic torsiograph including, an electrical signal generating means capable of generating an electrical signal of frequency directly proportional to the instantaneous angular velocity of a rotating mass, means for converting said alternating current signal into a square wave of equal frequency, means for differentiating said square Wave to produce pulses having a pulse repetition frequency proportional to said alternating current frequency, means for generating equal energy pulses from said first mentioned pulses whose pulse repetition frequency is proportional to said alternating current signal, means for detecting said equal energy pulses to obtain a signal equal in frequency to the torsional vibration beingv measured and means for integrating this last mentioned signal to produce a signal proportional in amplitude to the amplitude of the torsional oscillation being measured, and measuring means for said last mentioned signal to determine the torsional oscillation amplitude and frequency of said torsional oscillation.

3. In a non-seismic torsiograph including an electrical signal generating means capable of generating an electrical signal of frequency directly proportional to the instantaneous angular veloc-` ity of a rotating body, means for generating equal energy, unidirectional pulses from said rst mentioned signal Whose pulse repetition frequency is proportional to said alternating current signal, means for electrically detecting said equal energy pulses to obtain a signal, amplifying means connected to the detecting means, means to integrate the signal connected to the output of the amplifying means to produce a signal proportional in amplitude and equal in frequency to the torsional vibration being measured and measuring means connected to the integrating means.

LAWRENCE F. HOPE.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,396,540 Stanseld Mar. 12, 1946 2,399,635 Hope May 7, 1946 FOREIGN PATENTS Number Country Date 617,065 Great Britain Feb. 1, 1949 lil 

